Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 250315 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1015 PM EST Fri Feb 24 2017 .SYNOPSIS... High pressure over the Atlantic Ocean will maintain dry and unseasonably warm conditions through Saturday. A strong cold front will cross the region Saturday night, bringing showers and areas of fog. There will be a low chance for isolated thunderstorms as this front passes. Blustery conditions with temperatures close to seasonal normals expected for Sunday and Monday. A couple of weather systems will bring periods of wet weather Monday night into Thursday. Colder air looks to return late next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... Fog redeveloping along the South Coast. With dew points in the lower 50s, just shy of the extreme value for this date, the low levels are primed with moisture. A light south flow off 40 degree water provides enough refrigeration to saturate the airmass in the south. Otherwise a fair dry night. Light wind will allow locally dense fog in the usual spots and lighter fog elsewhere. Dew points in the lower 50s should support overnight min temps in the 50s. No changes planned to the forecast. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Not much change to expectations during this period. Low clouds and areas of fog likely to start Saturday. This will limit sunshine for a while, resulting in lower max temperatures, which will still be well above normal. Guidance has not been handling the warmth the past couple of days very well, so kept the trend of going a couple degrees higher than the warmest guidance. Still thinking a strong cold front will move across southern New England Saturday evening, about the same time as a potent mid level shortwave. Mid level lapse rates should be more unstable than moist adiabatic. So despite a climatologically unfavorable time, cannot completely rule out the possibility for a few thunderstorms during the evening and overnight hours. The greatest risk for thunderstorms would be across western MA and northern CT. Higher temperatures will lead to greater mixing depth of the boundary layer. This should lead to more gusty southwest winds of 25 to 30 kt, particularly toward the coast and over the coastal waters. Any convection could bring stronger gusts to the surface across the interior, too. Precipitable water values continue to show just over an inch, well above normal. But this is a narrow and fast-moving zone, so while showers may be briefly strong, total amounts should be 0.50 inches or less. Colder air rushes in late Saturday night behind a cold front. It will be a race between the cold air and the departing showers, but a brief changeover to snow is possible at the end. Any accumulations should be limited, generally less than an inch and mainly over the higher terrain of the Berkshires and Worcester Hills. Finally, the colder air advection behind the front will bring mixing of strong WNW winds aloft to the surface. Wind gusts will have a potential late Saturday night of reaching 30-40 knots. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Highlights... * Blustery and more seasonable temperatures Sun and Mon * Low pressure will bring scattered rain and/or snow showers Tue * Another low passes N of New England with rain showers possible Mon night through Wed night * A cold front may cause rain showers to mix or changing to snow showers Thursday Overview... Noting rather good agreement with the 12Z model suite on development and movement of weather features across the region into Tuesday. Beyond this, model solutions diverge, mainly due to continued progressive upper level steering flow across the lower 48, causing timing and track issues amongst the individual models. Appears the 12Z GFS is on the fast side of the guidance in moving systems along in the fast flow. Overall, looks like temps will continue to run warmer than seasonal normal, with the mildest temps around the Mon-Wed timeframe at this point. Signals beyond this appears to see a return to near or below normal temps by late next week. However, timing and track of the systems during that timeframe remain in question due to the fast steering flow aloft. Details... Sunday...High confidence. H5 trough pushes quickly offshore Sunday morning. Any leftover rain and/or snow showers over E coastal areas should be offshore by 13Z. High pressure ridge will approach from the W by Sunday evening. General W wind flow at the surface and aloft moves in. Noting H85 low level jet at 40 kt, and 30-35 kt below to H95. Excellent low level mixing in place with lapse rates at 9-10C/km up to H85. So, will likely see gusts up to up to 30-35 mph, possibly a bit higher across the higher inland terrain as well as along the coast. Even though colder air works in aloft, temps look to top off milder than seasonal normals. Highs will be mainly in the 40s, though could reach to around 50 in the coastal plain and lower CT valley. However, with the blustery winds, it will feel colder with wind chills in the 20s across the higher terrain and 30s elsewhere. Monday...Moderate to high confidence. High pressure ridge builds offshore as center of the associated high will push off the mid Atlantic coast. Winds back to SW during the day on the backside of the high. Another dry day with some gusty winds, up to 20-30 mph possible around midday or during the afternoon, highest along the S coast, Cape Cod and the islands. Mid and upper level moisture will start to work in aloft, so clouds will be increasing during the afternoon. Highs will range from the mid 40s across the higher inland terrain to around 50 across the coastal plain. Monday night through Wednesday...Moderate confidence. As mentioned above, model solutions begin to diverge during this timeframe. Noting high pressure settling off the SE U.S. coast. Mid level steering currents shift to a more SW direction with broad ridging over eastern Canada into the western Atlc. Noting weak short waves in this flow, with a wide variety of tracks for each individual wave. At the surface, will see low pressure wave shift NE in the mid level flow late Mon night and Tue. Most of the energy remains just offshore, but will see slug of moisture cross the region. have carried slight chance to chance POPs, with the best chance for showers during Tuesday. Looks like models signal mainly rain, but could see some mixed rain/snow showers at the onset of precip overnight Mon night. QPF values on order of 0.1 to 0.2 inches during Tuesday. Mild air remains in place on Tuesday, so highs will be in the mid 40s to around 50. Precip will linger Tue night as first wave moves off the Mass coast into the Gulf of Maine. However, another low looks to cross out of the Great Lakes into southern Quebec late Tue night into Wed bringing another slug of precip to the region. SW winds remain in place, so temps will not fall much Tue night. Lows will be mainly in the 30s. Could see a brief period of mixed rain/snow showers along the Mass/NH border overnight. On Wednesday, the low shifts E-NE, but another trailing front will keep the chance for precip across the region into Wed night, but timing is in question. Another question is whether a secondary low will form along this front as it pushes toward the mid Atlantic coast or even a bit further north. This could delay the exit of the precip. Expect highs in the upper 40s to mid 50s, so expect rain showers to continue. Thursday...Low confidence. Low pressure looks to push into eastern Canada, with trailing cold front passing offshore. May see lingering rain and/or snow showers before ending. Timing of front`s exact track exiting the region still very much in question. 12Z model suite and ensembles signaling colder air working across the region by Thu night. Temps will be cooler than earlier in the week, but will be close to seasonal normals. Friday...Low confidence. For now, should see mainly dry but cold and blustery conditions. Highs may run about 5 degrees below seasonal normals. && .AVIATION /03Z SATURDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/... Tonight...Moderate confidence. General background VFR. Area of IFR/LIFR lingers along the south coast. Fog patches develop in the interior with IFR/LIFR. Saturday...Moderate confidence. Lingering IFR in morning fog, otherwise VFR. Showers approach from the west and are most likely between 21Z and 03Z in the west, and between 00Z and 06Z in the east. Conditions may briefly lower to IFR in any rain showers. Isolated thunderstorms are possible as this band of showers moves through. Rain may change to snow across the higher terrain as it tapers off Saturday night. More LLWS is possible in the evening with S-SW winds at 40-50 knots at 2000-3000 feet AGL. Winds shift from the west during the early night as a cold front sweeps through from west to east. WNW winds will become gusty overnight with gusts to 30 to 35 knots possible. KBOS TAF...High confidence in TAF through 25/04Z. Moderate confidence in TAF after 25/04Z. KBDL TAF...High confidence in TAF through 25/04Z. Moderate confidence in TAF after 25/04Z. Outlook /Sunday through Wednesday/... Sunday...High confidence. VFR. W-NW wind gusts to 25-35 kt. Monday...High confidence. VFR. W-SW winds gusting to 20-25 kt, highest along the coast and over the higher terrain, diminishing Mon night. Monday night-Wednesday...Moderate confidence. Areas of MVFR conditions possible in -SHRA and/or -SHSN. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/...High confidence. Tonight...Winds and seas remain relatively light. South to southwest winds continue. Saturday...Moderate confidence. A cold front sweeps across the waters Saturday evening and early night with showers, and perhaps isolated thunderstorms. Strong winds aloft may produce a couple of strong wind gusts in any showers and storms. Winds shift behind this cold front. Winds from the west after midnight will have potential gusts of 30 to 35 knots. This would be borderline conditions for gales toward Sunday morning. Outlook /Sunday through Wednesday/... Sunday...High confidence. W winds gusting up to 25-30 kt. Some gust up to 35 kt possible mainly over the open waters. Gale watch in effect. Seas up to 6-8 ft. Winds and seas should slowly diminish Sun night. Good visibilities. Monday...High confidence. Winds back to SW gusting up to 25-30 kt highest on the eastern outer waters. Seas remain around 5 ft. Will likely hold on to small craft conditions through Mon night over the outer waters. Good visibilities. Tuesday through Wednesday...Low to moderate confidence. Expect E-SE winds gusting to 20 kt on Tue, then shifting to SW on Wednesday. Gusts will increase to around 25 kt late Wed/Wed night, along with seas building to at or above 5 ft over the open waters. With approaching system to the west could see lower vsbys in rain and fog. && .HYDROLOGY... We will need to monitor rising water levels across southern New England into early next week. Much, if not all, of our snowpack has, or will have, melted. There is still much more snowpack upstream, over northern new England, that will push into the headwaters and head downstream. Some river levels could approach action stage. && .CLIMATE... RECORD HIGH TEMPS FOR TODAY BOS 73/2017 - previous record 70/1985 PVD 72/1985 - topped off at 71 degrees BDL 73/1985 - topped off at 72 degrees ORH 69/2017 - previous record 67/1985 RECORD HIGH MIN TEMPS FOR TODAY BOS 49/1930 - bottomed out at 46 this morning (no record) PVD 45/1984 - bottomed out at 45 this morning BDL 43/1981 - bottomed out at 42 this morning (no record) ORH 46/1985 - bottomed out at 48 this morning RECORD HIGH TEMPS FOR SATURDAY BOS 65/1930 PVD 69/1976 BDL 70/1976 ORH 64/1976 RECORD HIGH MIN TEMPS FOR SATURDAY BOS 46/1891 PVD 45/1930 BDL 45/1930 ORH 37/1996, 1984, 1976 && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Gale Watch from late Saturday night through Sunday evening for ANZ230>237-250-251-254>256. && $$ SYNOPSIS...Belk/EVT NEAR TERM...WTB/Belk/EVT SHORT TERM...Belk LONG TERM...EVT AVIATION...Belk/EVT MARINE...Belk/EVT HYDROLOGY... CLIMATE...

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